Re: Sequential workflow in an asynchronous GWT world
Hello Robert I had the same problem in various GWT projects until I accidentally stumbled across a little used feature of GWT that completely changed the way I write GWT-apps now: history tokens. History tokens are used to implement control points in the application towards the user can jump at will, but are unfortunately perceived merely as walking-sticks to get bookmarks and the back button working. But if you think about it, history tokens can do so much more. Essentially they are a messaging mechanism between the view and the business logic. User-driven events (clicks on links, buttons etc) can be captured as history tokens and server-driven events (responses to RPC calls etc) can be covered by programmatically creating new history tokens. Thus you easily separate the sources of events (user actions, server actions) from the control logic and the view. In my applications I typically have four types of classes: 1. The data model which consists of POJOs containing the data the client works with 2. The service classes which consists of the business logic, client side validation and the communication with the server 3. The view which consists of widgets, render the data model and manipulate it. I can feed a model object into a view and get it back from the view, similar to the way Swing works. User actions in the view do _not_ call code from the service classes, but instead create History tokens. 4. The control logic. This is with regard to your question the most interesting part. It implements a HistoryListener and listens to events from the view and asynchronous events from the service classes. It knows the current state and based on the history item it receives via the listener can decide which view to manipulate or which service to call. Essentially, this is the implementation of a control flow. Hope that helps! G. On Mar 5, 4:15 am, rlaferla robertlafe...@comcast.net wrote: How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Re: Sequential workflow in an asynchronous GWT world
In general I think it is better to try to avoid this situation if possible - and often it is if you think about it for a bit - because a) the less RPC round trips you make the better, and b) the less callbacks you have in your client code the simpler it is. In general two good question to ask are: 1. Can the various logic branches be resolved automatically in the happy days use case on the server as a result of one call? Often they can if you look at things in a different way. If so you can then think about how to deal with edge cases. 2. How much of the server state would the client really need to know to successfully control the logic branches? Often less than you'd think at first. For example, it may be that in your app the first selections the user makes in this work flow are sufficient to generate a graph of permissible branches and/or additional required data values on the server from a single initial RPC call. In effect, create a simple model for your work flow process on the server and transfer it to the client up front. Thereafter the client could handle the UI dialog by itself until completed (with no horrible async callback interruptions and chains in the code) and then send the transaction details in one final RPC call. Of course this may not in the end be possible in your application, but it's worth looking into as it will increase performance and decrease complexity, as I think you have realized from your OP regards gregor. On Mar 5, 6:12 am, hazy1 matt.egyh...@gmail.com wrote: Making an async call appear to be sequential is easy, just block or fade out or have a pop up progress bar until the async operation completes. On Mar 4, 10:15 pm, rlaferla robertlafe...@comcast.net wrote: How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Sequential workflow in an asynchronous GWT world
How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Re: Sequential workflow in an asynchronous GWT world
You have to think about what kind of UI the users actions have caused. For instance, if you would expect all inputs to become disabled (or at least the one which would generate more async calls). Perhaps also some kind of waiting indicator that you are in an async call. On Wed, Mar 4, 2009 at 10:15 PM, rlaferla robertlafe...@comcast.net wrote: How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Re: Sequential workflow in an asynchronous GWT world
Sorry - so to make it more applicable to what you were asking: disable your current UI/indicate that the application is working. you may also want to prefetch the UI here if necessary. when you receive your result in your async callback, perform the transition. On Wed, Mar 4, 2009 at 10:32 PM, Vitali Lovich vlov...@gmail.com wrote: You have to think about what kind of UI the users actions have caused. For instance, if you would expect all inputs to become disabled (or at least the one which would generate more async calls). Perhaps also some kind of waiting indicator that you are in an async call. On Wed, Mar 4, 2009 at 10:15 PM, rlaferla robertlafe...@comcast.netwrote: How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
Re: Sequential workflow in an asynchronous GWT world
Making an async call appear to be sequential is easy, just block or fade out or have a pop up progress bar until the async operation completes. On Mar 4, 10:15 pm, rlaferla robertlafe...@comcast.net wrote: How is everyone managing to implement sequential workflows when GWT only allows async calls? I have a series of panels that user must respond to in sequence and their answers may lead to a different path of panels (warnings, error panels, etc..) I think every GWT programmer working on a large project must have run into this. I'm interested in what strategies/ techniques/code you used to help keep the complexity down. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google Web Toolkit group. To post to this group, send email to Google-Web-Toolkit@googlegroups.com To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Google-Web-Toolkit?hl=en -~--~~~~--~~--~--~---
